Section 538 (Audio System): General Description

The radio wave bands used in radio broadcasting are as follows:

Fig 1: Identifying Radio Wave Band Frequency Graph

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LF: Low Frequency

MF: Medium Frequency

HF: High Frequency

VHF: Very High Frequency

There are great differences in the size of the service area for AM and FM monaural. Sometimes FM stereo broadcasts cannot be received even through AM can be received in very clearly.

Not only does FM stereo have the smallest service area, but it also picks up static and other types of interference ("noise") easily.

Fig 2: Identifying Service Area

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Besides the problem of static, there are also the problems called "fading", "multipath" and "fade out". These problems are caused not by electrical noise but by the nature of the radio waves themselves.

1. Fading

   Besides electrical interference, AM broadcasts are also susceptible to other types of interference, especially at night. This is because AM radio waves bounce off the ionosphere at night. These radio waves then interfere with the signals from the same transmitter that reach the vehicle's antenna directly. This type of interference is called "fading".

   Fig 3: Identifying Fading Area

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2. Multipath

   One type of interference caused by the bounce of radio waves off of obstructions is called "multipath". Multipath occurs when a signal from the broadcast transmitter antenna bounces off buildings and mountains and interferes with the signal that is received directly.

   Fig 4: Identifying Multipath

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3. Fade Out

   Because FM radio waves are of higher frequencies than AM radio waves, they bounce off buildings, mountains, and other obstructions. For this reason, FM signals often seem to gradually disappear or fade away as the vehicle goes behind a building or other obstruction. This is called "fade out".

   Fig 5: Identifying Fade Out Area

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1. Questionnaire for noise:

   It is very important for noise trouble shooting to have good understanding of the claims from the customers. Refer to the following questionnaire to diagnose the problem accurately.

   NOISE PROBLEM TROUBLESHOOTING CHART
   
   

   AM	Noise occurs at a specific place.	Strong possibility of foreign noise.
   	Noise occurs when listening to faint broadcasting.	There is a possibility that the same program is broadcasted from different local stations, and the passenger may be listening the same program from other station (S).
   	Noise occurs only at night.	Strong possibility of the beat from a distant broadcasting.
   FM	Noise occurs while driving on a particular area.	Strong possibility of multipath noise and fading noise caused by the changes of FM waves.

   HINT:

   If the condition of noise occurrence does not meet any of the above questionnaire, check the problems referring to "Reception Problem" at step  3 .

2. Matters that require attention when checking:
   • Noise coming into the radio usually has no harm for daily use as the noise protection is taken, and it is very rare for an extremely loud noise to come in. When extremely loud noise comes into the radio, check if the grounding is normal where the antenna is installed.
   • Check if all the regular noise prevention parts are properly installed, and if there is any installation of non-authorized parts and non-authorized wiring.
   • If you leave the radio under out of tune (not turning), it is easy to diagnose the phenomenon as noise occurs frequently.
3. Antenna and noise:

Electronic signal received by the antenna will reach to the radio transmitted through the core wire of the coaxial cable. Any noise wave other than radio wave is mixed into this core wire, that naturally causes noise in the radio and poor sound quality. In order to prevent the noise from coming into radio, the core wire inside the coaxial cable is covered with a mesh wire called "shield wire" which transmits the noise to the ground.

Compact Disc Players use a laser beam pick-up to read the digital signals recorded on the CD and reproduce analog signals of the music, etc.

HINT:

Never attempt to disassemble or oil any part of the player unit. Do not insert any object other than a disc into the magazine.

MAINTENANCE 

1. Raise the cassette door with fingers.

   Then, using a pencil or similar object, push in the guide.

2. Using a cleaning pen or cotton applicator soaked in cleaner, clean the head surface, the pinch rollers and the capstans.
   Fig 6: Taping Player/Head Cleaning

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MAINTENANCE 

If the disc gets dirty, clean the disc by wiping the surface from the center to outside in the radial directions with a soft cloth.